The Small Computer System Interface (SCSI) input/output (I/O) bus is widely-used to connect peripheral devices, such as input and output interface devices and mass storage devices (e.g., disks and tapes), to small and medium-size computers, including to workstations and personal computers (PCs). As the complexity of applications that these computers support increases along with their power, there is arising a need to connect these computers to ever-more peripheral devices. Furthermore, as these computers come to support more mission-critical applications, the need for highly-reliable configurations (e.g., duplicated or redundant configurations) is becoming pronounced.
Unfortunately, the SCSI bus is not well suited to meet these needs. The standard SCSI bus has an addressing limit of eight device identifiers (IDs) and hence is limited to having only eight peripheral devices connected thereto. This number is reduced to only four distinct duplicated devices in a fault-tolerant application that relies on active-device redundancy. Furthermore, the SCSI bus standard requires each device ID to be unique.